Correlation between neuroanatomical and functional respiratory changes observed in an experimental model of Parkinson's disease

Targeted TGF-βR2 Knockdown in the Retrotrapezoid Nucleus Mitigates Respiratory Dysfunction and Cognitive Decline in a Mouse Model of Cerebral Amyloid Angiopathy with and without Stroke

Introduction

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of amyloid-beta peptides within cerebral blood vessels, leading to neurovascular complications. Ischemic strokes result from acute disruptions in cerebral blood flow, triggering metabolic disturbances and neurodegeneration. Both conditions often co-occur and are associated with respiratory dysfunctions. The retrotrapezoid nucleus (RTN), which is crucial for CO2 sensing and breathing regulation in the brainstem, may play a key role in breathing disorders seen in these conditions. This study aims to investigate the role of Transforming Growth Factor Beta (TGF-β) signaling in the RTN on respiratory and cognitive functions in CAA, both with and without concurrent ischemic stroke.

Methods

Adult male Tg-SwDI (CAA model) mice and C57BL/6 wild-type controls underwent stereotaxic injections of lentivirus targeting TGF-β2R2 in the RTN. Stroke was induced by middle cerebral artery occlusion using a monofilament. Respiratory functions were assessed using whole-body plethysmography, while cognitive functions were evaluated through the Barnes Maze and Novel Object Recognition Test (NORT). Immunohistochemical analysis was conducted to measure TGF-βR2 and GFAP expressions in the RTN.

Results

CAA mice exhibited significant respiratory dysfunctions, including reduced respiratory rates and increased apnea frequency, as well as impaired cognitive performance. TGF-βR2 knockdown in the RTN improved respiratory functions and cognitive outcomes in CAA mice. In CAA mice with concurrent stroke, TGF-βR2 knockdown similarly enhanced respiratory and cognitive functions. Immunohistochemistry confirmed reduced TGF-βR2 and GFAP expressions in the RTN following knockdown.

Conclusions

Our findings demonstrate that increased TGF-β signaling and gliosis in the RTN contribute to respiratory and cognitive dysfunctions in CAA and CAA with stroke. Targeting TGF-βR2 signaling in the RTN offers a promising therapeutic strategy to mitigate these impairments. This study is the first to report a causal link between brainstem gliosis and both respiratory and cognitive dysfunctions in CAA and stroke models.

State-dependent alteration of respiration in a rat model of Parkinson's disease

Parkinson's disease (PD) is the second most frequent neurodegenerative disorder. Besides major deficits in motor coordination, patients may also display sensory and cognitive impairments, which are often overlooked despite being inherently part of the PD symptomatology. Amongst those symptoms, respiration, a key mechanism involved in the regulation of multiple physiological and neuronal processes, appears to be altered. Importantly, breathing patterns are highly correlated with the animal's behavioral states. This raises the question of the potential impact of behavioral state on respiration deficits in PD. To answer this question, we first characterized the respiratory parameters in a neurotoxin-induced rat model of PD (6-OHDA) across three different vigilance states: sleep, quiet waking and exploration. We noted a significantly higher respiratory frequency in 6-OHDA rats during quiet waking compared to Sham rats. A higher respiratory amplitude was also observed in 6-OHDA rats during both quiet waking and exploration. No effect of the treatment was noted during sleep. Given the relation between respiration and olfaction and the presence of olfactory deficits in PD patients, we then investigated the odor-evoked sniffing response in PD rats, using an odor habituation/cross-habituation paradigm. No substantial differences were observed in olfactory abilities between the two groups, as assessed through sniffing frequency. These results corroborate the hypothesis that respiratory impairments in 6-OHDA rats are vigilance-dependent. Our results also shed light on the importance of considering the behavioral state as an impacting factor when analyzing respiration.

Impact of Serotonergic 5HT1A and 5HT2A Receptor Activation on the Respiratory Response to Hypercapnia in a Rat Model of Parkinson's Disease

In Parkinson's disease (PD), along with typical motor dysfunction, abnormal breathing is present; the cause of which is not well understood. The study aimed to analyze the effects of stimulation of the serotonergic system with 5-HT1A and 5-HT2A agonists in a model of PD induced by injection of 6-hydroxydopamine (6-OHDA). To model PD, bilateral injection of 6-OHDA into both striata was performed in male Wistar rats. Respiratory disturbances in response to 7% hypercapnia (CO2 in O2) in the plethysmographic chamber before and after stimulation of the serotonergic system and the incidence of apnea were studied in awake rats 5 weeks after 6-OHDA or vehicle injection. Administration of 6-OHDA reduced the concentration of serotonin (5-HT), dopamine (DA) and norepinephrine (NA) in the striatum and the level of 5-HT in the brainstem of treated rats, which have been associated with decreased basal ventilation, impaired respiratory response to 7% CO2 and increased incidence of apnea compared to Sham-operated rats. Intraperitoneal (i.p.) injection of the 5-HT1AR agonist 8-OH-DPAT and 5-HT2AR agonist NBOH-2C-CN increased breathing during normocapnia and hypercapnia in both groups of rats. However, it restored reactivity to hypercapnia in 6-OHDA group to the level present in Sham rats. Another 5-HT2AR agonist TCB-2 was only effective in increasing normocapnic ventilation in 6-OHDA rats. Both the serotonergic agonists 8-OH-DPAT and NBOH-2C-CN had stronger stimulatory effects on respiration in PD rats, compensating for deficits in basal ventilation and hypercapnic respiration. We conclude that serotonergic stimulation may have a positive effect on respiratory impairments that occur in PD.

TNFR1-mediated neuroinflammation is necessary for respiratory deficits observed in 6-hydroxydopamine mouse model of Parkinsońs Disease

Parkinson's Disease (PD) is characterized by classic motor symptoms related to movement, but PD patients can experience symptoms associated with impaired autonomic function, such as respiratory disturbances. Functional respiratory deficits are known to be associated with brainstem neurodegeneration in the mice model of PD induced by 6-hydroxydopamine (6-OHDA). Understanding the causes of neuronal death is essential for identifying specific targets to prevent degeneration. Many mechanisms can explain why neurons die in PD, and neuroinflammation is one of them. To test the influence of inflammation, mediated by microglia and astrocytes cells, in the respiratory disturbances associated with brainstem neurons death, we submitted wild-type (WT) and TNF receptor 1 (TNFR1) knockout male mice to the 6-OHDA model of PD. Also, male C57BL/6 animals were induced using the same PD model and treated with minocycline (45 mg/kg), a tetracycline antibiotic with anti-inflammatory properties. We show that degeneration of brainstem areas such as the retrotrapezoid nucleus (RTN) and the pre-Botzinger Complex (preBotC) were prevented in both protocols. Notably, respiratory disturbances were no longer observed in the animals where inflammation was suppressed. Thus, the data demonstrate that inflammation is responsible for the breathing impairment in the 6-OHDA-induced PD mouse model.

Update on vascular control of central chemoreceptors

At least four mechanisms have been proposed to elucidate how neurons in the retrotrapezoid (RTN) region sense changes in CO2 /H+ to regulate breathing (i.e., function as respiratory chemosensors). These mechanisms include: (1) intrinsic neuronal sensitivity to H+ mediated by TASK-2 and GPR4; (2) paracrine activation of RTN neurons by CO2 -responsive astrocytes (via a purinergic mechanism); (3) enhanced excitatory synaptic input or disinhibition; and (4) CO2 -induced vascular contraction. Although blood flow can influence tissue CO2 /H+ levels, there is limited understanding of how control of vascular tone in central CO2 chemosensitive regions might contribute to respiratory output. In this review, we focus on recent evidence that CO2 /H+ -induced purinergic-dependent vasoconstriction in the ventral parafacial region near RTN neurons supports respiratory chemoreception. This mechanism appears to be unique to the ventral parafacial region and opposite to other brain regions, including medullary chemosensor regions, where CO2 /H+ elicits vasodilatation. We speculate that this mechanism helps to maintain CO2 /H+ levels in the vicinity of RTN neurons, thereby maintaining the drive to breathe. Important next steps include determining whether disruption of CO2 /H+ vascular reactivity contributes to or can be targeted to improve breathing problems in disease states, such as Parkinson's disease.

Respiratory deficits in a female rat model of Parkinson's Disease

NEW FINDINGS

What is the central question of this study? How does 6-OHDA-induced Parkinson's Disease model affect the respiratory response in female rats? What effect does ovariectomy have on that response? What is the main finding and its importance? Our results suggest a protective effect of ovarian hormones in maintaining normal neuroanatomical integrity of the medullary respiratory nucleus in females. It was observed that ovariectomy alone reduced NK1r density in preBotc and BotC, and there was an incremental effect of 6-OHDA and ovariectomy on RTN neurons.

ABSTRACT

Emerging evidence indicates that Parkinson's disease (PD) courses with autonomic and respiratory deficiencies in addition to the classical motor symptoms. The prevalence of PD is lower in women, and it has been hypothesized that neuroprotection by ovarian hormones can explain this difference. While male PD animal models present changes in the central respiratory control areas, as well as ventilatory parameters under normoxia and hypercapnia, little is known about sex differences regarding respiratory deficits in this disease background. This study aimed to explore the neuroanatomical and functional respiratory changes in intact and ovariectomized female rats subjected to chemically induced PD via a bilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA). The respiratory parameters were evaluated by whole-body plethysmography, and the neuroanatomy was monitored using immunohistochemistry. It was found that dopaminergic neurons in the substantia nigra and neurokinin-1 receptor (NK1r) density in the rostral ventrolateral respiratory group, Botzinger and pre-Botzinger complex were reduced in the chemically induced PD animals. Additionally, reduced numbers of Phox2b neurons were only observed in the retrotrapezoid nucleus of PD-ovariectomized rats. Concerning respiratory parameters, in ovariectomized rats, the resting and hypercapnia-induced tidal volume (V_T ) is reduced, and ventilation (V_E ) changes independently of 6-OHDA administration. Notably, there is a reduction in the number of RTN phox2b neurons and hypercapnia-induced respiratory changes in PD-ovariectomized animals due to a 6-OHDA and OVX interaction. These results suggest a protective effect induced by ovarian hormones in neuroanatomical changes observed in a female experimental PD model. This article is protected by copyright. All rights reserved.

Regulation of blood vessels by ATP in the ventral medullary surface in a rat model of Parkinson's disease

Parkinson's disease (PD) patients often experience impairment of autonomic and respiratory functions. These include conditions such as orthostatic hypotension and sleep apnea, which are highly correlated with dysfunctional central chemoreception. Blood flow is a fundamental determinant of tissue CO₂/H⁺, yet the extent to which blood flow regulation within chemoreceptor regions contributes to respiratory behavior during neurological disease remains unknown. Here, we tested the hypothesis that 6-hydroxydopamine injection to inducing a known model of PD results in dysfunctional vascular homeostasis, biochemical dysregulation, and glial morphology of the ventral medullary surface (VMS). We show that hypercapnia (FiCO₂ = 10%) induced elevated VMS pial vessel constriction in PD animals through a P2-receptor dependent mechanism. Similarly, we found a greater CO₂-induced vascular constriction after ARL67156 (an ectonucleotidase inhibitor) in control and PD-induced animals. In addition, we also report that weighted gene correlational network analysis of the proteomic data showed a protein expression module differentially represented between both groups. This module showed that gene ontology enrichment for components of the ATP machinery were reduced in our PD-model compared to control animals. Altogether, our data indicate that dysfunction in purinergic signaling, potentially through altered ATP bioavailability in the VMS region, may compromise the RTN neuroglial vascular unit in a PD animal model.

Respiratory Abnormalities in Parkinson's Disease: What Do We Know from Studies in Humans and Animal Models?

Parkinson’s disease (PD) is the second most common progressive neurodegenerative disease characterized by movement disorders due to the progressive loss of dopaminergic neurons in the ventrolateral region of the substantia nigra pars compacta (SNpc). Apart from the cardinal motor symptoms such as rigidity and bradykinesia, non-motor symptoms including those associated with respiratory dysfunction are of increasing interest. Not only can they impair the patients’ quality of life but they also can cause aspiration pneumonia, which is the leading cause of death among PD patients. This narrative review attempts to summarize the existing literature on respiratory impairments reported in human studies, as well as what is newly known from studies in animal models of the disease. Discussed are not only respiratory muscle dysfunction, apnea, and dyspnea, but also altered central respiratory control, responses to hypercapnia and hypoxia, and how they are affected by the pharmacological treatment of PD.

Respiratory disorders of Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra, mainly affecting people over 60 yr of age. Patients develop both classic symptoms (tremors, muscle rigidity, bradykinesia, and postural instability) and nonclassical symptoms (orthostatic hypotension, neuropsychiatric deficiency, sleep disturbances, and respiratory disorders). Thus, patients with PD can have a significantly impaired quality of life, especially when they do not have multimodality therapeutic follow-up. The respiratory alterations associated with this syndrome are the main cause of mortality in PD. They can be classified as peripheral when caused by disorders of the upper airways or muscles involved in breathing and as central when triggered by functional deficits of important neurons located in the brainstem involved in respiratory control. Currently, there is little research describing these disorders, and therefore, there is no well-established knowledge about the subject, making the treatment of patients with respiratory symptoms difficult. In this review, the history of the pathology and data about the respiratory changes in PD obtained thus far will be addressed.

Breathing disorders in neurodegenerative diseases

Neurodegenerative disorders are a diverse group of conditions caused by progressive degeneration of neurons resulting in cognitive, motor, sensory, and autonomic dysfunction, leading to severe disability and death. Pulmonary dysfunction is relatively common in these conditions, may be present early in the disease, and is less well recognized and treated than other symptoms. There are variable disorders of upper and lower airways, central control of ventilation, strength of respiratory muscles, and breathing during sleep which further impact daily activities and quality of life and have the potential to injure vulnerable neurons. Laryngopharyngeal dysfunction affects speech, swallowing, and clearance of secretions, increases the risk of aspiration pneumonia, and can cause stridor and sudden death. In Parkinson's disease, L-Dopa benefits some pulmonary symptoms but there are limited pharmacological treatment options for pulmonary dysfunction. Targeted treatments include strengthening of respiratory muscles, positive airway pressure in sleep and techniques to improve cough efficacy. Well-designed clinical trials are needed to evaluate the long-term benefits of these interventions. Challenges for the future include earlier identification of pulmonary dysfunction in the clinic, institution of the most effective treatments (based on clinical trials that measure long-term meaningful outcomes) and the development of neuroprotective treatment.

Inhibition of anandamide hydrolysis does not rescue respiratory abnormalities observed in an animal model of Parkinson's disease

NEW FINDINGS

What is the central question of this study? The respiratory frequency to hypercapnia is attenuated in an animal model of Parkinson's disease (PD): what is the therapeutic potential of inhibition of anandamide hydrolysis for this respiratory deficit? What is the main finding and its importance? In an animal model of PD there is an increased variability in resting respiratory frequency and an impaired tachypnoeic response to hypercapnia, which is accompanied by diminished expression of Phox2b immunoreactivity in the retrotrapezoid nucleus (RTN). Inhibition of anandamide hydrolysis also impaired the response to hypercapnia and decreased the number of Phox2b immunoreactive cells in the RTN. This strategy does not reverse the respiratory deficits observed in an animal model of PD.

ABSTRACT

Parkinson's disease (PD) is characterized by severe classic motor symptoms along with various non-classic symptoms. Among the non-classic symptoms, respiratory dysfunctions are increasingly recognized as contributory factors to complications in PD. The endocannabinoid system has been proposed as a target to treat PD and other neurodegenerative disorders. Since symptom management of PD is mainly focused on the classic motor symptoms, in this work we aimed to test the hypothesis that increasing the actions of the endocannabinoid anandamide by inhibiting its hydrolysis with URB597 reverses the respiratory deficits observed in an animal model of PD. Results show that bilateral injection of 6-hydroxydopamine hydrochloride (6-OHDA) in the dorsal striatum leads to neurodegeneration of the substantia nigra, accompanied by reduced expression of Phox2b in the retrotrapezoid nucleus (RTN), an increase in resting respiratory frequency variability and an impaired tachypnoeic response to hypercapnia. URB597 treatment in control animals was associated with an impaired tachypnoeic response to hypercapnia and a reduced expression of Phox2b in the RTN, whereas treatment of 6-OHDA-lesioned animals with URB597 was not able to reverse the deficits observed. These results suggest that targeting anandamide may not be a suitable strategy to treat PD since this treatment mimics the respiratory deficits observed in the 6-OHDA model of PD.

Review: Neuropathology findings in autonomic brain regions in SUDEP and future research directions

Autonomic dysfunction is implicated from clinical, neuroimaging and experimental studies in sudden and unexpected death in epilepsy (SUDEP). Neuropathological analysis in SUDEP series enable exploration of acquired, seizure-related cellular adaptations in autonomic and brainstem autonomic centres of relevance to dysfunction in the peri-ictal period. Alterations in SUDEP compared to control groups have been identified in the ventrolateral medulla, amygdala, hippocampus and central autonomic regions. These involve neuropeptidergic, serotonergic and adenosine systems, as well as specific regional astroglial and microglial populations, as potential neuronal modulators, orchestrating autonomic dysfunction. Future research studies need to extend to clinically and genetically characterized epilepsies, to explore if common or distinct pathways of autonomic dysfunction mediate SUDEP. The ultimate objective of SUDEP research is the identification of disease biomarkers for at risk patients, to improve post-mortem recognition and disease categorisation, but ultimately, for exposing potential treatment targets of pharmacologically modifiable and reversible cellular alterations.

6-hydroxydopamine and ovariectomy has no effect on heart rate variability parameters of females

OBJECTIVES

In addition to the classic motor symptoms of Parkinson's disease (PD), patients also present with non-motor symptoms, such as autonomic dysfunction, which is present in almost 90% of patients with PD, affecting the quality of life and mortality. Regarding sex differences in prevalence and presentation, there is increasing concern about how sex affects autonomic dysfunction. However, there are no previous data on autonomic cardiac function in females after 6-hydroxydopamine (6-OHDA) striatal injection.

METHODS

Wistar female rats were ovariectomized. After 20 days, the animals received bilateral injections of 6-OHDA (total dose per animal: 48 µg) or a vehicle solution in the striatum. Thirty days after 6-OHDA injection, subcutaneous electrodes were implanted for electrocardiogram (ECG) recording. Ten days after electrode implantation, ECG signals were recorded. Analyses of heart rate variability (HRV) parameters were performed, and the 6-OHDA lesion was confirmed by analyzing the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta (SNpc).

RESULTS

A high dose of 6-OHDA did not affect HRV of females, independent of ovariectomy. As expected, ovariectomy did not affect HRV or lesions in the SNpc after 6-OHDA injection.

CONCLUSIONS

We suggest that females with 6-OHDA present with cardioprotection, independent of ovarian hormones, which could be related to female vagal predominance.

Sleep disturbance in movement disorders: insights, treatments and challenges

Sleep and circadian rhythm disturbances are central features of many movement disorders, exacerbating motor and non-motor symptoms and impairing quality of life. Understanding these disturbances to sleep is clinically important and may further our understanding of the underlying movement disorder. This review evaluates the current anatomical and neurochemical understanding of normal sleep and the recognised primary sleep disorders. In addition, we undertook a systematic review of the evidence for disruption to sleep across multiple movement disorders. Rapid eye movement sleep behaviour disorder has emerged as the most reliable prodromal biomarker for the alpha synucleinopathies, including Parkinson's disease and multiple system atrophy, often preceding motor symptom onset by several years. Abnormal sleep has also been described for many other movement disorders, but further evidence is needed to determine whether this is a primary or secondary phenotypic component of the underlying condition. Medication used in the treatment of motor symptoms also affects sleep and can aggravate or cause certain sleep disorders. Within the context of movement disorders, there is also some suggestion of a shared underlying mechanism for motor and sleep pathophysiology, with evidence implicating thalamic and brainstem structures and monoaminergic neurotransmission. This review highlights the need for an understanding of normal and abnormal sleep within the movement disorder clinic, an ability to screen for specific causes of poor sleep and to treat sleep disturbance to improve quality of life. Key sleep disorders also act as important biomarkers and have implications in diagnosis, prognosis and the development of future therapies.

Unraveling the Mechanisms Underlying Irregularities in Inspiratory Rhythm Generation in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder anatomically characterized by a progressive loss of dopaminergic neurons in the substantia nigra compacta (SNpc). Much less known, yet clinically very important, are the detrimental effects on breathing associated with this disease. Consistent with the human pathophysiology, the 6-hydroxydopamine hydrochloride (6-OHDA) rodent model of PD shows reduced respiratory frequency (fR) and NK1r-immunoreactivity in the pre-Bötzinger complex (preBötC) and PHOX2B+ neurons in the retrotrapezoid nucleus (RTN). To unravel mechanisms that underlie bradypnea in PD, we employed a transgenic approach to label or stimulate specific neuron populations in various respiratory-related brainstem regions. PD mice were characterized by a pronounced decreased number of putatively rhythmically active excitatory neurons in the preBötC and adjacent ventral respiratory column (VRC). Specifically, the number of Dbx1 and Vglut2 neurons was reduced by 47.6% and 17.3%, respectively. By contrast, inhibitory Vgat+ neurons in the VRC, as well as neurons in other respiratory-related brainstem regions, showed relatively minimal or no signs of neuronal loss. Consistent with these anatomic observations, optogenetic experiments identified deficits in respiratory function that were specific to manipulations of excitatory (Dbx1/Vglut2) neurons in the preBötC. We conclude that the decreased number of this critical population of respiratory neurons is an important contributor to the development of irregularities in inspiratory rhythm generation in this mouse model of PD.SIGNIFICANCE STATEMENT We found a decreased number of a specific population of medullary neurons which contributes to breathing abnormalities in a mouse model of Parkinson's disease (PD).

Parafacial neurons in the human brainstem express specific markers for neurons of the retrotrapezoid nucleus

The retrotrapezoid nucleus (RTN) is a hub for respiratory chemoregulation in the mammal brainstem that integrates chemosensory information from peripheral sites and central relays. Chemosensitive neurons of the RTN express specific genetic and molecular determinants, which have been used to identify RTN precise location within the brainstem of rodents and nonhuman primates. Based on a comparative approach, we hypothesized that among mammals, neurons exhibiting the same specific molecular and genetic signature would have the same function. The co-expression of preprogalanin (PPGAL) and SLC17A6 (VGluT2) mRNAs with duplex in situ hybridization has been studied in formalin fixed paraffin-embedded postmortem human brainstems. Two specimens were processed and analyzed in line with RTN descriptions in adult rats and macaques. Double-labeled PPGAL+/SLC17A6+ neurons were only identified in the parafacial region of the brainstem. These neurons were found surrounding the nucleus of the facial nerve, located ventrally to the nucleus VII on caudal sections, and slightly more dorsally on rostral sections. The expression of neuromedin B (NMB) mRNA as a single marker of chemosensitive RTN neurons has not been confirmed in humans. The location of the RTN in human adults is provided. This should help to develop investigation tools combining anatomic high-resolution imaging and respiratory functional investigations to explore the pathogenic role of the RTN in congenital or acquired neurodegenerative diseases.

Respiratory Dysfunctions in Parkinson's Disease Patients

Respiratory dysfunctions have been associated with Parkinson's disease since the first observations of the disease in 1817. Patients with Parkinson's disease frequently present respiratory disorders with obstructive ventilatory patterns and restrictive modifications, as well as limitations in respiratory volumes. In addition, respiratory impairments are observed due to the rigidity and kyphosis that Parkinson's disease patients experience. Subsidiary pulmonary complications can also appear as side effects of medication. Silent aspiration can be the cause of pneumonia in Parkinson's disease. Pulmonary dysfunction is one of the main factors that leads to the morbidity and mortality of patients with Parkinson's disease. Here, we performed a narrative review of the literature and reviewed studies on dyspnea, lung volumes, respiratory muscle function, sleep breathing disorders, and subsidiary speech and swallow impairments related to pulmonary dysfunction in patients with Parkinson's disease.

Respiratory dysfunction in Parkinson's disease: a narrative review

The presence of respiratory symptoms in Parkinson's disease (PD) has been known since the first description of the disease, even though the prevalence and incidence of these disturbances are not well defined. Several causes have been reported, comprising obstructive and restrictive pulmonary disease and changes in the central ventilatory control, and different pathogenetic mechanisms have been postulated accordingly. In our review, we encompass the current knowledge about respiratory abnormalities in PD, as well as the impact of anti-Parkinsonian drugs as either risk or protective factors. A description of putative pathogenetic mechanisms is also provided, and possible treatments are discussed, focusing on the importance of recognising and treating respiratory symptoms as a key manifestation of the disease itself. A brief description of respiratory dysfunctions in atypical Parkinsonism, especially α-synucleinopathies, is also provided.

This review addresses current knowledge about respiratory dysfunctions in Parkinson's disease, from the aetiopathology to pharmacological and invasive treatments, describing the different clinical phenotypeshttps://bit.ly/2X7OLtN

Stimulation of retrotrapezoid nucleus Phox2b-expressing neurons rescues breathing dysfunction in an experimental Parkinson's disease rat model

Emerging evidence from multiple studies indicates that Parkinson's disease (PD) patients suffer from a spectrum of autonomic and respiratory motor deficiencies in addition to the classical motor symptoms attributed to substantia nigra degeneration of dopaminergic neurons. Animal models of PD show a decrease in the resting respiratory rate as well as a decrease in the number of Phox2b-expressing retrotrapezoid nucleus (RTN) neurons. The aim of this study was to determine the extent to which substantia nigra pars compact (SNc) degeneration induced RTN biomolecular changes and to identify the extent to which RTN pharmacological or optogenetic stimulations rescue respiratory function following PD-induction. SNc degeneration was achieved in adult male Wistar rats by bilateral striatal 6-hydroxydopamine injection. For proteomic analysis, laser capture microdissection and pressure catapulting were used to isolate the RTN for subsequent comparative proteomic analysis and Ingenuity Pathway Analysis (IPA). The respiratory parameters were evaluated by whole-body plethysmography and electromyographic analysis of respiratory muscles. The results confirmed reduction in the number of dopaminergic neurons of SNc and respiratory rate in the PD-animals. Our proteomic data suggested extensive RTN remodeling, and that pharmacological or optogenetic stimulations of the diseased RTN neurons promoted rescued the respiratory deficiency. Our data indicate that despite neuroanatomical and biomolecular RTN pathologies, that RTN-directed interventions can rescue respiratory control dysfunction.

Astrocytes in the nucleus of the solitary tract: Contributions to neural circuits controlling physiology

The nucleus of the solitary tract (NTS) is the primary brainstem centre for the integration of physiological information from the periphery transmitted via the vagus nerve. In turn, the NTS feeds into downstream circuits regulating physiological parameters. Astrocytes are glial cells which have key roles in maintaining CNS tissue homeostasis and regulating neuronal communication. Recently an increasing number of studies have implicated astrocytes in the regulation of synaptic transmission and physiology. This review aims to highlight evidence for a role for astrocytes in the functions of the NTS. Astrocytes maintain and modulate NTS synaptic transmission contributing to the control of diverse physiological systems namely cardiovascular, respiratory, glucoregulatory, and gastrointestinal. In addition, it appears these cells may have a role in central control of feeding behaviour. As such these cells are a key component of signal processing and physiological control by the NTS.

Pilocarpine-induced status epilepticus reduces chemosensory control of breathing

One of the possible causes of death in epilepsy is breathing disorders, especially apneas, which lead to an increase in CO₂ levels (hypercapnia) and/or a decrease in O₂ levels in arterial blood (hypoxemia). The respiratory neurons located in the ventral brainstem respiratory column are the main groups responsible for controlling breathing. Recent data from our group demonstrated respiratory changes in two experimental models of epilepsy, i.e. audiogenic epilepsy, and amygdala rapid kindling. Here, we aimed to evaluate respiratory changes in the classic model of temporal lobe epilepsy induced by intra-hippocampal injection of pilocarpine. Adult Wistar rats with stainless-steel cannulas implanted in the hippocampus region were used. The animals were submitted to pilocarpine injection (2.4 mg/μL, N = 12-15) or saline (N = 9) into the hippocampus. The respiratory parameters analyzed by whole-body plethysmography were respiratory rate (f_R), tidal volume (V_T) and ventilation (V_E). Respiratory mechanics such as Newtonian airway resistance (R_n), viscance of the pulmonary parenchyma (G) and the elastance of the pulmonary parenchyma (H) were also investigated. No changes in baseline breathing were detected 15 or 30 days after pilocarpine-induced status epilepticus (SE). However, 30 days after pilocarpine-induced SE, a significant reduction in V_E was observed during hypercapnic (7% CO₂) stimulation, without affecting the hypoxia (8% O₂) ventilatory response. We also did not observe changes in respiratory mechanics. The present results suggest that the impairment of the hypercapnia ventilatory response in pilocarpine-induced SE could be related to a presumable degeneration of brainstem respiratory neurons but not to peripheral mechanisms.

Characterisation of medullary astrocytic populations in respiratory nuclei and alterations in sudden unexpected death in epilepsy

Central failure of respiration during a seizure is one possible mechanism for sudden unexpected death in epilepsy (SUDEP). Neuroimaging studies indicate volume loss in the medulla in SUDEP and a post mortem study has shown reduction in neuromodulatory neuropeptidergic and monoaminergic neurones in medullary respiratory nuclear groups. Specialised glial cells identified in the medulla are considered essential for normal respiratory regulation including astrocytes with pacemaker properties in the pre-Botzinger complex and populations of subpial and perivascular astrocytes, sensitive to increased pCO_2, that excite respiratory neurones. Our aim was to explore niches of medullary astrocytes in SUDEP cases compared to controls. In 48 brainstems from three groups, SUDEP (20), epilepsy controls (10) and non-epilepsy controls (18), sections through the medulla were labelled for GFAP, vimentin and functional markers, astrocytic gap junction protein connexin43 (Cx43) and adenosine A1 receptor (A1R). Regions including the ventro-lateral medulla (VLM; for the pre-Bötzinger complex), Median Raphe (MR) and lateral medullary subpial layer (MSPL) were quantified using image analysis for glial cell populations and compared between groups. Findings included morphologically and regionally distinct vimentin/Cx34-positive glial cells in the VLM and MR in close proximity to neurones. We noted a reduction of vimentin-positive glia in the VLM and MSPL and Cx43 glia in the MR in SUDEP cases compared to control groups (p < 0.05-0.005). In addition, we identified vimentin, Cx43 and A1R positive glial cells in the MSPL region which likely correspond to chemosensory glia identified experimentally. In conclusion, altered medullary glial cell populations could contribute to impaired respiratory regulatory capacity and vulnerability to SUDEP and warrant further investigation.

Respiratory disturbances in a mouse model of Parkinson's disease

NEW FINDINGS

What is the central question of this study? Clinical reports have described and suggested central and peripheral respiratory abnormalities in Parkinson's disease (PD) patients; however, these reports have never addressed the occurrence of these abnormalities in an animal model. What is the main finding and its importance? A mouse model of PD has reduced neurokinin-1 receptor immunoreactivity in the pre-Bӧtzinger complex and Phox2b-expressing neurons in the retrotrapezoid nucleus. The PD mouse has impairments of respiratory frequency and the hypercapnic ventilatory response. Lung collagen deposition and ribcage stiffness appear in PD mice.

ABSTRACT

Parkinson's disease (PD) is a neurodegenerative motor disorder characterized by dopaminergic deficits in the brain. Parkinson's disease patients may experience shortness of breath, dyspnoea, breathing difficulties and pneumonia, which can be linked as a cause of morbidity and mortality of those patients. The aim of the present study was to clarify whether a mouse model of PD could develop central brainstem and lung respiratory abnormalities. Adult male C57BL/6 mice received bilateral injections of 6-hydroxydopamine (10 μg μl^-1 ; 0.5 μl) or vehicle into the striatum. Ventilatory parameters were assessed in the 40 days after induction of PD, by whole-body plethysmography. In addition, measurements of respiratory input impedance (closed and opened thorax) were performed. 6-Hydroxydopamine reduced the number of tyrosine hydroxylase neurons in the substantia nigra pars compacta, the density of neurokinin-1 receptor immunoreactivity in the pre-Bӧtzinger complex and the number of Phox2b neurons in the retrotrapezoid nucleus. Physiological experiments revealed a reduction in resting respiratory frequency in PD animals, owing to an increase in expiratory time and a blunted hypercapnic ventilatory response. Measurements of respiratory input impedance showed that only PD animals with the thorax preserved had increased viscance, indicating that the ribcage could be stiff in this animal model of PD. Consistent with stiffened ribcage mechanics, abnormal collagen deposits in alveolar septa and airways were observed in PD animals. Our data showed that our mouse model of PD presented with neurodegeneration in respiratory brainstem centres and disruption of lung mechanical properties, suggesting that both central and peripheral deficiencies contribute to PD-related respiratory pathologies.

Glucose Homeostasis Is Not Affected in a Murine Model of Parkinson's Disease Induced by 6-OHDA

There is a mutual relationship between metabolic and neurodegenerative diseases. However, the causal relationship in this crosstalk is unclear and whether Parkinson’s disease (PD) causes a posterior impact on metabolism remains unknown. Considering that, this study aimed to evaluate the appearance of possible changes in metabolic homeostasis due to 6-hydroxydopamine (6-OHDA) administration, a neurotoxin that damage dopaminergic neurons leading to motor impairments that resemble the ones observed in PD. For this, male Wistar rats received bilateral 6-OHDA administration in the dorsolateral striatum, and the motor and metabolic outcomes were assessed at 7, 21, or 35 days post-surgical procedure. Dexamethasone, a diabetogenic glucocorticoid (GC), was intraperitoneally administered in the last 6 days to challenge the metabolism and reveal possible metabolic vulnerabilities caused by 6-OHDA. Controls received only vehicles. The 6-OHDA-treated rats displayed a significant decrease in locomotor activity, exploratory behavior, and motor coordination 7 and 35 days after neurotoxin administration. These motor impairments paralleled with no significant alteration in body mass, food intake, glucose tolerance, insulin sensitivity, and biochemical parameters (plasma insulin, triacylglycerol, and total cholesterol levels) until the end of the experimental protocol on days 35–38 post-6-OHDA administration. Moreover, hepatic glycogen and fat content, as well as the endocrine pancreas mass, were not altered in rats treated with 6-OHDA at the day of euthanasia (38th day after neurotoxin administration). None of the diabetogenic effects caused by dexamethasone were exacerbated in rats previously treated with 6-OHDA. Thus, we conclude that bilateral 6-OHDA administration in the striatum causes motor deficits in rats with no impact on glucose and lipid homeostasis and does not exacerbate the adverse effects caused by excess GC. These observations indicate that neurodegeneration of dopaminergic circuits in the 6-OHDA rats does not affect the metabolic outcomes.